Biomech: Musculo-skeletal

• Anatomical reference position:

  • Upright standing position
  • Facing forward
  • Legs together
  • Feet flat on floor
  • Hands at side with palms facing forward
• Anatomical reference planes:

  • Frontal (coronal)
  • Transverse (horizontal)
  • Sagittal (median)
  • Cardinal planes: 3 imaginary perpendicular reference planes that divide the body in half by mass
• Fundamental Movements in different planes:

  • Sagittal Plane about a Mediolateral Axis: Flexion (angle diminishes) and Extension (angle increases)
  • Frontal Plane about an Anteroposterior Axis: Abduction (away from the body) and Adduction (towards the body)
  • Transverse Plane about a Longitudinal Axis: Rotation left/right (neck, trunk)
• Function of the skeleton includes:

  • Movement
  • Muscle attachment
  • Providing levers

  
  

  • Support
  • Shape

  
  

  • Protection of vital organs

  
  

  • Physiological functions like Ca2+ regulation, endocrine regulation, and blood cell production in the bone marrow
• Bone composition:

  • Organic component (35%): Matrix mostly type 1 collagen, cells like osteoblasts, osteocytes, osteoclasts
  • Inorganic component (65%): Mineral content like hydroxyapatite
• General structure of the bone:

  • Long bones consist of a diaphysis (shaft) and two epiphyses
  • Metaphysis is where the epiphyseal line or growth plate resides
• Bone growth and development:

  • Longitudinal growth occurs at the epiphyseal plates and stops around 18-20 years
  • Circumferential/radial growth increases diameter throughout lifespan
• Bone response to stress:

  • Wolff’s Law: bone adapts its form to the load placed upon it
  • Bone remodeling involves osteocyte signaling, osteoblast bone formation, and osteoclast bone resorption in response to load
• Types of joints:

  • Synarthroses: immovable joints like sutures of the skull
  • Amphiarthrosis: slightly movable joints like synchondroses and symphyses
  • Diarthroses (synovial): freely movable joints like gliding/plane, hinge, pivot, condyloid, saddle, and ball and socket joints
• A LEVER is a relatively rigid object that may be made to rotate about an axis by the application of force

  
• Levers in muscles

  
• Different lever classes in the body

  
• Types of bones

  
• Bone Remodelling: Hypertrophy

  An increase in bone mass due to predominance of osteoblast activity.

  • Response to regular physical activity

  Tennis players have muscular and bone hypertrophy in playing arm.

  • The greater the habitual load, the more mineralization of the bone

  Also relates to amount of impact of activity/sport
• Bone remodelling: Atrophy

  A decrease in bone mass resulting from a predominance osteoclast activity

  • Decrease in

  Bone calcium

  Bone mass and strength

  • Seen in bed ridden patients, sedentary elderly, and astronauts
• Axial skeleton: 74 bones

  Appendicular skeleton: 126 bones

  
• Classification of bones by shape:

  • Flat bones: Thin, curved bone; serve as a point of attachment for muscles, protects internal organs
  • Short bones: Cube-shaped bone that is approximately equal in length, width, and thickness; provides limited motion
  • Long bones: Cylinder-shaped bone that is longer than it is wide; functions as a lever
  • Sesamoid bones: Embedded within tendons to protect them from stress
  • Irregular bones: Bone of complex shape; protects internal organs from compressive forces

  
• Joint function:

  • To facilitate movement between bones
  • To transmit force from one bone to another
• • Synarthroses: joints that don't move, like sutures of the skull

  
• • Amphiarthrosis: joints that slightly move, like synchondroses and symphyses
  • Attenuate forces and permit some motion between adjacent bones

  
• • Diarthroses (Synovial): joints that freely move, including:

  
• • Gliding/Plane: flat articulating surfaces permitting non-axial gliding (e.g, joints between the carpals and tarsals)

  
• • Hinge: uni-axial movement with strong collateral ligaments restricting single axis hinge-like movement (uni-axial)
  • One convex and one concave articulating surface
  • e.g. Distal interphalangeal joints, proximal interphalangeal joints

  
• • Pivot: Rotation joints that permit rotation around one axis (uni-axial) like proximal and distal radioulnar joints

  
• • Condyloid: bi-axial movement like metacarpophalangeal joints
  • Ovoid articular surface allowing movement around two axes (bi-axial)

  
• • Saddle: tri-axial movement like carpometacarpal joint of the thumb
  • Similar to condyloid but greater range of motion due to saddle shape of both bones (tri-axial)

  
• • Ball and Socket: tri-axial rotation joints

  
• Articular cartilage is a protective layer of connective tissue that covers the ends of articulating bones

  • Reduces stress by distributing force
  • Reduces friction and wear

  
• Articular capsule:

  • Double layered membrane that surrounds every synovial joint

  Synovial membrane:

  • Lines the deep surface of the capsule, secretes synovial fluid

  
• Joint Stability:

  • Ability of a joint to resist abnormal displacement of the articulating bones
  • Provided by;
  • Shape of articulating bone surfaces
  • Arrangements of ligaments and muscles
  • Other connective tissues

  
• Skeletal muscles:

  • Are the only component of the musculoskeletal system that can actively generate force
  • Are active organs, which can be voluntarily and involuntarily stimulated
  • Create internal forces to hold the position of the body or create movement
  • Are attached to bones (via tendons) and cross a joint (or joints)
  • Make up approx 40% of body mass
• Properties of the skeletal muscle:

  Excitability -

  • The ability to respond to stimulation

  Extensibility - Passive

  • The ability to stretch beyond the resting length

  Elasticity - Passive

  • The ability to return to its resting length

  Contractility - Active

  • The ability to contract generate tension at the ends
• Properties of the skeletal muscles : pt 2

  • Muscles can extend or shorten 40-50% of the original resting length
  • In the context of muscle 'contract' refers to producing force
  • Tension and force are used interchangeably
• Muscle tendon

  
• Structure of the muscle
• Microscopic organisation of a muscle fibre:

  • Muscle cells have more nuclei
  • Sarcoplasm is the cytoplasm of the muscular cell. It includes also glycogen and other fuels
  • Mitochondria (cell metabolism)
  • Myofibril contractile apparatus
  • Membranous system (sarcoplasmic reticulum, T tubule (TT))

  
• Myofibril: Made up of many sarcomeres

  
• Mechanism of muscle contraction:

  • Action potential (AP) travels along the sarcolemma
  • AP enters cell at Transverse Tubule (TT) and triggers release of Calcium into the cell
  • Calcium binds with troponin causing tropomyosin to "unblock" the actin filaments
  • Myosin heads bind with actin to form cross bridges and complete the power stroke (moving actin filaments closer together)
  • ATP fuels the pumping back of Calcium into the SR which 're-sets' the system
• The amount of force developed in a muscle is directly proportional to the number of cross-bridges formed
• Sarcomeres always want to shorten, and the external force dictates changes in muscle (or MTU) length